Current drive and current control devices are well known in the art. Such devices operate to maintain a given magnitude of current along a particular current path for the purpose of stabilizing the operating current (iD) delivered to a respective load. One use for such devices is to provide stabilized current to a light emitting diode (LED). As will be appreciated by those skilled in the art, the brightness of an LED is as a function of the amount of current passing through the LED. To stabilize the brightness of an LED, one must stabilize the current passing through the LED. Prior art patents in the field of current control and stabilized LED operation include U.S. Pat. No. 4,160,934 issued Jul. 10, 1979 to Kirsch; U.S. Pat. No. 5,025,204 issued Jun. 18, 1991 to Su; U.S. Pat. No. 6,097,360 issued Aug. 1, 2000 to Holloman; and U.S. Pat. No. 6,954,039 issued Oct. 11, 2005 to Lin et al.
While stabilized current control in support of LED operation is a laudable pursuit, many current applications require dynamic brightness control for individual LEDs and/or LED arrays. One such application is an optical light engine using LEDs in support of a digital micro-mirror device (DMD) image projection system. In such LED based image projection systems, it is often desirable and frequently necessary to dynamically adjust the individual brightness of one or a plurality of high power LEDs used as projector light sources. LED drive circuits designed to provide stable and/or static brightness control fall short of producing a wide dynamic range of LED brightness control. Therefore, the need exists for LED drive circuitry that permits selective and dynamic LED brightness control. Furthermore, there is a need to provide brightness control circuits that offer advantages in compactness, simplicity, low cost, and speed of operation.
The above and other features and advantages of the invention will be further understood from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.